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A method for generating a reinforcement schedule that closely approximates idealized VI schedules in which reinforcement assignments occur randomly in time (RI schedules) is described. Response rates of pigeons exposed for 20 sessions to this schedule appeared very similar to response rates characteristic of arithmetic series VIs. The distribution function describing these schedules was derived and its relations to other VI distributions, as well as to FI and random ratio (RR) were shown.

A set of four manipulanda were presented to four Cebus monkeys, individually, and later in pairs. Step 1 provided an estimate of each S's probability of operating each item, while Step 2 determined whether pairing the items would disturb the ordinal relations among individual response probabilities. Both procedures provided information necessary for testing the assumption that a reinforcer is simply a contingent response whose independent probability of occurrence is greater than that of the associated instrumental response. Step 3 tested this assumption by again presenting pairs of items, but with one locked and its operation made contingent upon operation of the free item of the pair. The four Ss differed markedly in the extent to which the items produced different independent response probabilities, and correspondingly, in the extent to which the contingent pairs subsequently produced reinforcement. Confirmation of the present assumptions came primarily from one S, which differed substantially on the individual items, and showed five cases of reinforcement, all in the predicted direction. Further, reinforcement was shown by an increase in both contingency and extinction sessions. Finally, the response of intermediate probability reinforced the response of least, but not the one of greatest, probability, indicating that a reinforcer cannot be identified absolutely, but only relative to the base response.

Two pre‐schedule‐change stimuli were superimposed on the same VI baseline and were thereby equated with respect to reinforcement potential. One such stimulus preceded a transition to an extinction schedule or a VI schedule of lower reinforcement frequency while the other preceded a transition to a VI schedule of higher reinforcement frequency. It was found that response rate during the warning stimulus was greater preceding the transition to the lower reinforcement frequency than it was preceding the transition to the higher reinforcement frequency. That difference was often evidenced by an absolute increase and decrease in rate, in conformity with previous findings on the topic. The present experiment extends previous findings in several ways, including the presentation of quantitative estimates of the effects.

Three pigeons, previously trained to a high level of accuracy on matching‐to‐sample procedures, were exposed to various schedules of ratio reinforcement for correct matches. Overall accuracy was lower on fixed ratio than on regular reinforcement. There was a high incidence of errors immediately after reinforcement on fixed ratio schedules with accuracy increasing as the ratio progressed. This increase was found to be inversely correlated with the latency of the observing response to the sample. By contrast, accuracy was high throughout the ratio on a variable ratio schedule.

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This paper describes a procedure for gaining experimental control over mediating behavipr on a spaced‐responding schedule of food reinforcement. Three rats, food‐deprived, were trained on a DRL 16 sec schedule of food reinforcement. Then, a concurrent schedule of food reinforcement was introduced on a second (mediating) lever, such that the first response to occur on the mediating lever, after the DRL interval had timed out, was reinforced with food, as was the next response to occur on the DRL lever. Reinforcement via the mediating lever became a discriminative stimulus for a food‐reinforcement opportunity on the DRL lever. Next, food reinforcement for the mediating behavior was replaced by a conditioned reinforcer consisting of onset of a buzzer signaling timing‐out of the DRL interval. Under these conditions, chaining of behavior on the two levers was strong, and timing on the DRL lever was more accurate than under ordinary DRL conditions. As the DRL requirement was lengthened from 16 sec to 24 sec to 60 sec, mediating behavior weakened slightly. When the inter‐response requirement for food reinforcement on the DRL lever was made shorter than the inter‐response requirement for conditioned reinforcement on the mediating lever, the mediating behavior extinguished. Performance in the experiment was analyzed into a four‐component chain, and the factors contributing to the maintenance, and later extinction, of mediating behavior are discussed.

The effects of cost (point‐loss per response) upon human avoidance, escape, and avoidance‐escape behavior maintained by PLPs (point‐loss periods) were investigated. Cost had a marked but differentially suppressive effect upon responding under all schedules. The greatest number of PLPs taken under cost occurred on the escape schedule. In most instances PLPs were more frequent on the avoidance‐escape schedule than on the avoidance schedule under cost. Inferior avoidance performance appeared only under cost conditions. Under no‐cost, all subjects (Ss) successfully avoided all PLPs after the first hour of conditioning. These results indicate that the development and maintenance of human avoidance and escape behavior may, in part, be dependent upon response cost conditions. Aversive control of human operant behavior may be limited without an adequate specification of response‐cost conditions.

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